The present invention relates to ophthalmic instruments referred to as refractors and more particularly to a refractor having a simplified cylinder lens assembly for more efficient and economic servicing thereof.
Commonly, an ophthalmic instrument referred to as a refractor is employed for efficiently carrying out optical analysis. Typical refractors include a right and a left battery, each having an eye position for the patient before which any of a broad variety of disk mounted testing lenses may be positioned. These lenses may be spherical, exhibiting a broad range of powers, or cylindrical, again exhibiting power variations but with respect to alignment along plus and minus axes. The cylindrical lenses may be used in the well-known Jackson cross-cylinder technique wherein the utilization of two cylinders off axis further is contrasted against a third spherocylindrical combination. The Jackson cross-cylinder test has been recognized as most beneficial to analysis and has been implemented broadly in ophthalmic refractors. An excellent explanation of the Jackson cross-cylinder test can be found in commonly assigned application Ser. No. 513,707 filed on July 14, 1983, of Marlin O. Thurston, now U.S. Pat. No. 4,523,822, the disclosure of which expressly is incorporated herein by reference.
Implementation of the Jackson cross-cylinder test in ophthalmic refractors has sparked various techniques for improving the accuracy of such test while reducing the burden and chance of error of the clinician administering such test. One such technique is the synchronization of the cross-cylinder lens in a manner wherein the axes of the cylinder lens and cross-cylinder lens are aligned in parallel at all times throughout administration of such ophthalmic evaluation. Initial efforts at developing such synchronization can be shown in U.S. Pat. Nos. 3,498,699 and 3,860,330, for example. Such techniques employ mechanical gear trains which link control knob means to the cylinder lens assemblies and to the cross-cylinder lens assembly whereby their axes remain parallel at all times. A much improved technique for such cross-cylinder synchronization involve optical encoding as described by Marlin O. Thurston in commonly-assigned application Ser. No. 513,707, cited above. Regardless of whether a mechanical or an electronic approach to the cross-cylinder synchronization is employed, all ophthalmic refractors must be serviced periodically for maintaining their efficiency and useful life. Moreover, mechanical defects often must be remedied in the refractor.
Servicing of ophthalmic refractors necessarily involves the skill of a trained technician who must be able to diagnose the instruments malady as well as repair same. For routine and warranty servicing, as well as for correction of defects in the instrument, repair time often dictates the ultimate cost involved in the reparation task. In this connection, disassembly of the refractor often is a simple task with the main burden of servicing falling upon reassembly. Reassembly of the instrument necessarily involves the realignment and timing of all mechanisms within the refractor so that accuracy and synchronization is maintained. For refractors which have the noted cross-cylinder synchronization feature, alignment of the timing of the instrument is even more critical.
The present invention provides a simplified assembly technique of the cylinder lens assemblies which is mechanically more reliable as well as simpler to service.